Exhaust gas purifying catalyst

Abstract

An exhaust gas purifying catalyst having a refractory three-dimensional structure coated with a catalytically active component comprising at least one kind of noble metals, a refractory inorganic oxide, and a zirconium oxide containing cerium and lanthanum, the crystal structure of the zirconium oxide containing cerium and lanthanum being a tetragonal structure of zirconium oxide.

What is claimed is:  
     
       1. An exhaust gas purifying catalyst comprising: 
       a catalytically active component comprising at least one kind of noble metals, a refractory inorganic oxide, and a zirconium oxide containing cerium and lanthanum; and  
       a refractory three-dimensional structure coated with the catalytically active component;  
       wherein said zirconium oxide containing cerium and lanthanum has a tetragonal crystal structure of zirconium oxide, a weight ratio of cerium as CeO 2  to zirconium as ZrO 2  in the range of 1:8 to 1:1, and a weight ratio of lanthanum as La 2 O 3  to zirconium as ZrO 2  in the range of 1:1.5 to 1:60.  
     
     
       2. A catalyst according to  claim 1 , wherein the noble metal is at least one member selected from the group consisting of palladium, platinum, rhodium and a mixture thereof. 
     
     
       3. A catalyst according to  claim 1 , wherein the refractory inorganic oxide is at least one member selected from the group consisting of alumina, titania, zirconia, silica, alumina-titania, alumina-zirconia, titania-zirconia and a mixture thereof. 
     
     
       4. A catalyst according to  claim 1 , wherein an amount of the noble metal comprises from 0.05 to 30 g per liter of said structure. 
     
     
       5. A catalyst according to  claim 4 , wherein the amount of the noble metal comprises from 0.15 to 20 g per liter of said structure. 
     
     
       6. A catalyst according to  claim 1 , wherein an amount of the refractory inorganic oxide comprises from 10 to 300 g per liter of the structure. 
     
     
       7. A catalyst according to  claim 6 , wherein the amount of the refractory inorganic oxide comprises from 50 to 250 g per liter of the structure. 
     
     
       8. A catalyst according to  claim 1 , wherein an amount of the zirconium oxide containing cerium and lanthanum comprises from 5 to 250 g per liter of the structure. 
     
     
       9. A catalyst according to  claim 8 , wherein the amount of the zirconium oxide containing cerium and lanthanum comprises from 10 to 200 g per liter of the structure. 
     
     
       10. A catalyst according to  claim 1 , wherein the weight ratio of cerium as CeO 2  to zirconium as ZrO 2  is in the range of 1:5 to 1:1. 
     
     
       11. A catalyst according to claim l, wherein the weight ratio of lanthanum as La 2 O 3  to zirconium as ZrO 2  is in the range of 1:1.5 to 1:40. 
     
     
       12. A catalyst according to  claim 1 , which further comprises an alkaline earth metal oxide. 
     
     
       13. A catalyst according to  claim 12 , wherein the alkaline earth metal oxide includes the oxides of barium, magnesium, calcium, strontium or a mixture thereof. 
     
     
       14. A catalyst according to  claim 12 , wherein an amount of the alkaline earth metal oxide is in the range of 0.1 to 50 g per liter of the structure. 
     
     
       15. A catalyst according to  claim 14 , wherein the amount of the alkaline earth metal oxide is in the range of 1 to 30 g per liter of the structure. 
     
     
       16. A method for simultaneous purification of carbon monoxide, hydrocarbon, and nitrogen oxide contained in the exhaust gas emitted from an internal combustion engine by the use of an exhaust gas purifying catalyst comprising: a catalytically active component comprising at least one kind of noble metals, a refractory inorganic oxide, and a zirconium oxide containing cerium and lanthanum; and a refractory three-dimensional structure coated with the catalytically active component; wherein said zirconium oxide containing cerium and lanthanum has a crystal structure of a tetragonal structure of zirconium oxide, a weight ratio of cerium as CeO 2  to zirconium as ZrO 2  in the range of 1:8 to 1:1, and a weight ratio of lanthanum as La 2 O 3  to zirconium ZrO 2  in the range of 1:1.5 to 1:60.